In my post last week I started to examine issues around frequency selection for wireless power systems. This week I want to take the discussion a bit further and talk about the benefits (as we perceive) of using lower frequencies (in the kHz range) vs. higher frequencies (MHz) as an industry standard.
As the standards debate rages on, different parties continue to put forward their various interpretations on the ideal frequency range. Various standards utilize higher frequency ranges than others. PowerbyProxi, through the CEA working group, continues to argue that standards that use lower frequency ranges (kHz) are more appropriate based on what we believe is in the best interest for you – the consumer.
There are several factors that need to be taken into account.
Complexity. How complex is the device to manufacture. Controllers used for wireless power systems are far more complex at the MHz range ultimately impacting the cost of manufacture and thus the price that the end-consumer (you) pays.
Interference. As we as we are aware there are no wireless devices operating in the MHz range that meet EMC radiated emission compliance. What it means is that at the moment, there is no proof that they wont cause interference on other devices.
Other factors such as charging distance, transmission efficiency, thermal properties and form factor tend to be implementation specific or require further research to be able to draw clear comparisons.
On the balance of the research done so far, lower frequencies at the kHz allow for more user friendly and functional wireless power systems to be developed. Isn’t that ultimately what it should be all about?
EMC radiation standards are used to qualify electronic devices against interference with other electronic devices. A piece of wire that has a current running through it will generate electric and magnetic fields – “H-field” emissions measure the magnetic component and “E-fields” emissions measure the electric component. EMC radiation standards ensure that these fields do not interact with other electronic devices to impair their operation.
EMC radiation standards were really designed to control and limit the amount of interference in long distance radio communication. The current standards regulating EMC radiation have been great at regulating these devices, however you now have a new type of electronic device that intentionally generates magnetic fields – those that use wireless power. Such electronic devices were never foreseen when these standards were written.
Consequently, there is one potential aspect of wireless power solutions (read more about wireless power here) which is not currently being regulated. This is the amount of electromotive force (EMF) that can be generated in a device which is in very close proximity. EMF is basically a fancy term for voltage! Electronics are sensitive to over-voltage (some more than others) and over-voltage can cause permanent damage to devices.
Sure there is a limit on how much “H-field” you can emit however these fields are typically measured using an antenna at a few meters or feet away from a device under test. The reading from the antenna and compliance to limits will not really tell you whether your shiny new smart-phone placed on your laptop’s wireless power supply is going to fail.
But hey at least your wireless power supply doesn’t mess with your FM radio…